Fuel cell assembly

ABSTRACT

A fuel cell assembly comprising an enclosure having a fuel cell stack mounted therein, and an inlet opening into the enclosure. The fuel cell stack having an inlet face for receiving coolant/oxidant fluid. The fuel cell assembly further comprises a delivery gallery extending from the inlet in the enclosure to the inlet face of the fuel cell stack, the delivery gallery having a first region and a second region separated by an aperture. The delivery gallery and aperture are configured such that, in use, coolant/oxidant fluid within the first region of the delivery gallery is turbulent, and coolant/oxidant fluid within the second region of the delivery gallery has a generally uniform pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International patent applicationPCT/GB2013/050096, filed on Jan. 17, 2013, which claims priority toGreat Britain Patent Application No. 1202591.2, filed on Feb. 15, 2012,the disclosures of which are incorporated by reference in theirentirety.

The invention relates to fuel cell assemblies, in particular toenclosures for mounting open cathode fuel cell stacks.

Conventional electrochemical fuel cells convert fuel and oxidant,generally both in the form of gaseous streams, into electrical energyand a reaction product. A common type of electrochemical fuel cell forreacting hydrogen and oxygen comprises a polymeric ion (proton) transfermembrane, with fuel and air being passed over respective sides of themembrane. Protons (i.e. hydrogen ions) are conducted through themembrane, balanced by electrons conducted through a circuit connectingthe anode and cathode of the fuel cell. To increase the availablevoltage, a stack may be formed comprising a number of such membranesarranged with separate anode and cathode fluid flow paths. Such a stackis typically in the form of a block comprising numerous individual fuelcell plates held together by end plates at either end of the stack.

Because the reaction of fuel and oxidant generates heat as well aselectrical power, a fuel cell stack requires cooling once an operatingtemperature has been reached. Cooling may be achieved by forcing airthrough the cathode fluid flow paths. In an open cathode stack, theoxidant flow path and the coolant path are the same, i.e. forcing airthrough the stack both supplies oxidant to the cathodes and cools thestack.

Providing uniform air delivery to the cathode electrode surfaces withina fuel cell can be challenging when using compact assemblies. The use ofplenum profiles and volumes may not be possible with tight volumetricpackaging constraints.

According a first aspect of the invention, there is provided a fuel cellassembly comprising:

-   -   an enclosure having a fuel cell stack mounted therein,    -   an inlet opening into the enclosure,    -   the fuel cell stack having an inlet face for receiving        coolant/oxidant fluid,    -   a delivery gallery extending from the inlet in the enclosure to        the inlet face of the fuel cell stack,    -   the delivery gallery having a first region and a second region        separated by an aperture,    -   wherein the delivery gallery and aperture are configured such        that, in use, coolant/oxidant fluid within the first region of        the delivery gallery is turbulent, and coolant/oxidant fluid        within the second region of the delivery gallery has a generally        uniform pressure.

Such a fuel cell assembly can advantageously provide turbulent flow inthe first region of the delivery gallery which can be used to cool anycomponents located in the first region, and also provide generallyuniform pressure in the second region such that the coolant/oxidant canbe uniformly applied to the layers in the fuel cell stack.

The aperture may define a restriction to flow between the first andsecond regions of the delivery gallery. The aperture may represent areduction in cross-sectional area in the flow path of thecoolant/oxidant flow between the first and second regions of thedelivery gallery. In this way, a pressure change experienced by theoxidant/coolant as it flows through the aperture can cause theoxidant/coolant to have a generally uniform pressure along the length ofthe fuel cell stack.

The aperture may extend in a longitudinal direction. The aperture may bein the vicinity of an end face of the fuel cell stack or an edge betweentwo faces of the fuel cell stack. The longitudinal direction of theaperture may extend along the edge between two faces of the fuel cellstack. These two faces of the fuel cell stack may be a bottom end faceand an inlet face, or a top end face and an outlet face.

The width of the aperture may vary in the longitudinal direction, whichmay assist in providing a uniform air pressure in the second region. Thewidth of the aperture may vary uniformly or non-uniformly in thelongitudinal direction. The width of the aperture may be a function of adistance from a fan or air flow generator. The aperture may get wider inthe longitudinal direction away from a fan or air flow generator. Thiscan be advantageous in equalising the air pressure in the second region,even though the air pressure in the first region can be lower atpositions further away from the fan or air flow generator.

The aperture may be defined, at least in part, by an end face of thefuel cell stack and optionally a protrusion extending towards the endface of the fuel cell stack. The end face of the fuel cell stack may bea bottom end face. The protrusion may extend away from an internal wallof the enclosure, and in some examples may comprise part of an internalwall of the enclosure. Providing the aperture in this way can enable thetransition between the first region and second region to be located inthe vicinity of the end of the stack. The second region may be defined,at least in part, by the inlet face of the fuel cell stack. The firstregion may be independent of the inlet face of the fuel cell stack.

The fuel cell assembly may comprise a diffuser within the first regionof the delivery gallery. The diffuser may be configured to impartturbulence on oxidant/coolant received from the inlet of the enclosure.The diffuser may be fixed such that it is not free to move in normal useof the fuel cell assembly. Such a diffuser can provide a convenientmeans of imparting turbulence that does not require any moving parts oractive components that may be more susceptible to damage and may consumepower.

The diffuser may comprise one or more fuel cell control systemcomponents, such as a printed circuit board (PCB), disposed within thedelivery gallery. In this way, particularly efficient cooling of thefuel cell control system components can be achieved without requiringany additional components.

The fuel cell assembly may further comprise a fan or air flow generatorlocated within the enclosure configured to cause the coolant/oxidant tobe transferred from the inlet in the enclosure to the inlet face of thefuel cell stack. The axis of the fan may be directed away from, orotherwise may not point towards, the aperture. This can encourageturbulent flow in the first region of the delivery gallery as thecoolant/oxidant encounters one or more components to diffuse the flow asit proceeds to the aperture to the second region of the deliverygallery.

The axis of the fan may be perpendicular or transverse to the plane ofthe layers in the stack. The axis of the fan may be perpendicular to thedirection of coolant/oxidant flow through the stack. Aligning the fanand fuel stack in this way can provide a compact fuel cell assembly andencourage turbulent flow of the coolant/oxidant in the first region.

The fuel cell stack may comprise an outlet face for expelling saidcoolant/oxidant fluid,

-   -   the fuel cell stack further including a pair of end faces        extending transversely between the inlet face and outlet face,    -   the enclosure defining a flow path for the coolant/oxidant fluid        that is configured to guide the coolant/oxidant fluid to the        inlet face, from the outlet face, and over at least one of the        end faces.

There may be provided a fuel cell assembly comprising:

-   -   an enclosure having a fuel cell stack mounted therein,    -   the fuel cell stack having an inlet face for receiving        coolant/oxidant fluid and an outlet face for expelling said        coolant/oxidant fluid,    -   the fuel cell stack further including a pair of end faces        extending transversely between the inlet face and outlet face,    -   the enclosure defining a flow path for the coolant/oxidant fluid        that is configured to guide the coolant/oxidant fluid to the        inlet face, from the outlet face, and over at least one of the        end faces.

Providing the coolant/oxidant flow path in this way can improve thecooling of the fuel cell stack and provide a compact enclosure.

The enclosure may define the flow path for the coolant/oxidant fluid toguide the coolant oxidant/fluid over both the end faces. This canimprove the cooling effect of the fuel cell stack even further.

The enclosure may define an exhaust gallery extending over and adjacentto one end face of the fuel cell stack. The enclosure may further defineat least one exhaust port at an edge or corner of the enclosure. An edgecan be considered as the meeting of two sides or surfaces and a cornercan be considered as the meeting of three sides or surfaces of theenclosure.

Providing the at least one exhaust port at an edge or corner of theenclosure can help to prevent the port from being blocked when theassembly is placed next to other objects; the ports can be considered asprotected because of their location.

The exhaust gallery may be at least partly defined by the outlet face ofthe fuel cell stack, a top end face of the fuel cell stack, and one ormore internal surfaces of the enclosure. In this way, theoxidant/coolant can be exposed to the top end face of the fuel cellstack before it exits the assembly through the exhaust port.

The edge or corner of the enclosure defining said at least one exhaustport may be disposed at or beyond a peripheral edge of the fuel cellstack. This can enable the oxidant/coolant to flow over a largeproportion of the end face of the fuel cell stack before exiting theexhaust port.

The at least one exhaust port may extend around more than one edge ofthe enclosure. Providing a relatively large exhaust port can enableacceptable performance of the fuel cell stack to be maintained when theexhaust port is partially obscured.

The fuel cell assembly may further comprise a separation wall configuredto separate the delivery gallery from an exhaust gallery. At least partof the separation wall may be movable so as to selectively provide anopening between the delivery gallery and the exhaust gallery. This canenable recirculation of the warm exhaust coolant/oxidant to the deliverygallery, thereby pre-heating the coolant/oxidant that is provided to theinlet face of the fuel cell stack.

The at least part of the separation wall may be moveable in accordancewith the temperature of the coolant/oxidant in the exhaust galleryand/or delivery gallery. In this way, recirculation can be selectivelyprovided to improve the performance of the fuel cell stack.

The fuel cell assembly may further include fuel cell control systemcomponents disposed within the exhaust gallery. In this way, the flowpath of the oxidant/coolant can be used to cool the fuel cell controlsystem components.

The enclosure may define a delivery gallery extending over and adjacentto one end face of the fuel cell stack. The enclosure may further defineat least one inlet port at an edge or corner of the enclosure. Providingthe at least one inlet port at an edge or corner of the enclosure canhelp to prevent the port from being blocked when the assembly is placednext to other objects; the ports can be considered as protected becauseof their location.

The delivery gallery may be defined at least in part by the inlet faceof the fuel cell stack, a bottom end face of the fuel cell stack, andone or more internal surfaces of the enclosure. In this way, theoxidant/coolant can be exposed to the bottom end face of the fuel cellstack before it enters the fuel cell stack.

The edge or corner of the enclosure defining said at least one inletport may be disposed at or beyond a peripheral edge of the fuel cellstack. This can enable the oxidant/coolant to flow over a largeproportion of the end face of the fuel cell stack before entering thefuel cell stack.

The at least one inlet port may extend around more than one edge of theenclosure. Providing a relatively large inlet port can enable acceptableperformance of the fuel cell stack to be maintained when the inlet portis partially obscured.

The fuel cell assembly may further include fuel cell control systemcomponents disposed within the delivery gallery. In this way, the flowpath of the oxidant/coolant can be used to cool the fuel cell controlsystem components.

The walls of the fuel cell stack may be generally parallel with thewalls of the enclosure. This can provide a compact assembly.

The fuel cell assembly may further comprise a fan or air flow generatorlocated within the enclosure configured to cause the coolant/oxidant tobe transferred along the flow path. The axis of the fan may beperpendicular or transverse to the plane of the layers in the stack. Theaxis of the fan may also be perpendicular to the direction ofcoolant/oxidant flow through the stack. Aligning the fan and fuel stackin this way can provide a compact fuel cell assembly.

The fuel cell assembly may comprise:

-   -   an inlet opening into the enclosure,    -   a delivery gallery extending from the inlet in the enclosure to        the inlet face of the fuel cell stack,    -   the delivery gallery having a first region and a second region        separated by an aperture,    -   wherein the delivery gallery and aperture are configured such        that, in use, coolant/oxidant fluid within the first region of        the delivery gallery is turbulent, and coolant/oxidant fluid        within the second region of the delivery gallery has a generally        uniform pressure.

According to a further aspect, there is provided a portable electronicdevice charging unit comprising any fuel cell assembly disclosed herein.

The invention will now be described by way of example, and withreference to the accompanying drawings in which:

FIG. 1a shows a schematic plan view of a fuel cell assembly according toan embodiment of the invention;

FIG. 1b shows an end cross-sectional view of the assembly on line b-b ofFIG. 1a ; and

FIG. 1c shows a side cross-sectional view of the assembly on line c-c ofFIG. 1 a.

Embodiments disclosed herein relate to a fuel cell assembly comprisingan enclosure having a fuel cell stack mounted therein.

In some examples, the fuel cell assembly has a delivery galleryextending from an inlet in the enclosure to an inlet face of the fuelcell stack, the delivery gallery having a first region and a secondregion separated by an aperture. The delivery gallery and aperture areconfigured such that, in use, air within the first region of thedelivery gallery is turbulent, and air within the second region of thedelivery gallery has a generally uniform pressure. This can enableeffective cooling of electronic components located in the first regiondue to the turbulent air flow, whilst also providing efficient use ofthe fuel cell stack as air is distributed evenly between layers in thefuel cell stack.

Alternatively, or additionally, the enclosure defines a flow path forair through the fuel stack that guides the air over at least one endface of the stack. Guiding the air in this way can provide additionalcooling to the stack and thermally decouple the stack from theenclosure. The fuel cell assembly may have a delivery gallery such thatair can be passed over a bottom end face of the stack before entering aninlet face of the stack and/or an exhaust gallery such that air thatleaves the stack through an outlet face can be passed over a top endface of the stack before exiting the assembly.

FIGS. 1a, 1b and 1c illustrate a fuel cell assembly 100 according to anembodiment of the invention. FIG. 1a shows a top view of the assembly100. FIG. 1b shows a cross-sectional view perpendicular to the assembly100 along the line b-b in FIG. 1a . FIG. 1c shows a cross-sectional viewlongitudinal to the assembly 100 along the line c-c in FIG. 1 a.

The fuel cell assembly 100 has an enclosure 102 having a fuel cell stack104 mounted therein. The walls of the fuel cell stack 104 are generallyparallel with the walls of the enclosure 102. The fuel cell stack 104has an inlet face 106 for receiving fluid, such as coolant or oxidantfluid. The fluid may be air, and will be referred to as air for the restof the description of FIGS. 1a, 1b and 1c . The fuel cell stack 104 alsohas an outlet face 108 for expelling the air. The inlet face 106 andoutlet face 108 are opposing faces of the fuel cell stack 104. In theexample of FIG. 1, the inlet and outlet faces 106, 108 can be consideredas longitudinal side faces of the fuel cell stack 104.

The fuel cell stack 104 also has end faces extending transverselybetween the inlet face 106 and the outlet face 108. The fuel cell stackhas a top end face 110 and a bottom end face 112 on opposing sides ofthe fuel cell stack 104. The top and bottom end faces 110, 112 arelocated parallel to the planes of the layers that make up the stack 104.The fuel cell stack 104 also has two side end faces 114, 116 on opposingsides of the fuel cell stack 104. The side end faces 114, 116 aretransverse to the planes of the layers that make up the fuel cell stack104.

The enclosure 102, at least in part, defines a flow path for guiding theair over at least one of the end faces 110, 112, 114, 116 and mostpreferably at least the top and bottom end faces 110, 112. Arrowsindicating the direction of air flow through the assembly 100 areincluded in FIGS. 1a to 1c . In this way, additional cooling can beprovided to the fuel cell stack 104. Also, a compact assembly 100 can beprovided.

Furthermore, the coupling of heat generated by the fuel cell stack 104to the enclosure 102 can be reduced as the fuel cell stack issubstantially detached from the enclosure 102. This can be particularlyadvantageous for examples where the enclosure is made from a heatconducting material such as aluminium. Such enclosures may have amaximum operating temperature. Therefore, detaching the fuel cell stack104 from the enclosure 102 by providing regions of the delivery gallery128 and/or exhaust gallery 126 therebetween can help to keep thetemperature of the enclosure 102 below its maximum operatingtemperature.

A thermal coating (not shown) may be provided on one or more of theinside surfaces of the enclosure 102 that define the exhaust gallery 126in order to thermally isolate the heat in the exhaust air from theenclosure 102.

In this example, the top surface of the enclosure 102 comprises a baffle118 that is spaced apart from the side walls of the enclosure 102 inorder to provide an opening into the enclosure 102 around the perimeterof the baffle 118. As will be discussed below, the opening around thebaffle 118 can provide inlet and exhaust ports 120, 122 for the air onthe edges or corners of the enclosure 102. An edge of the assembly 100can be considered as the meeting of two surfaces such as the baffle 118and a side wall of the enclosure 102. A corner of the assembly 100 canbe considered as the meeting of three surfaces such as the baffle 118and two side walls of the enclosure 102.

Providing the inlet and exhaust ports 120, 122 in this way can helpprotect them from becoming blocked, for example if objects are placed ontop of, or to the side of, the assembly 100.

As can be seen from FIG. 1a , substantially all of the opening aroundthe baffle 118 can be used as either an inlet port 120 or an exhaustport 122, although this need not necessarily be the case. An advantageof having relatively large inlet and exhaust ports 120, 122 is that thestack 104 can function adequately when either one or both of the ports120, 122 are partially obscured, for example up to 50% obscured.

The exhaust port 122 extends around the portion of the baffle 118 thatis generally located above the stack 104. In this way, when the airexits the outlet face 108 of the stack 104 it exits the enclosure 102through one or more of:

-   -   a region of the exhaust port that is next to the outlet face 108        of the stack—this region of the exhaust port is shown with        reference 122 a in FIGS. 1a and 1 b;    -   a region of the exhaust port that is next to the inlet face 106        of the stack 104—this region of the exhaust port is shown with        reference 122 b in FIGS. 1a and 1b ; and    -   a region of the exhaust port that is next to a side end face 116        of the stack 104—this region of the exhaust port is shown with        reference 122 c in FIGS. 1a and 1 c.

The baffle 118 is spaced apart from the top end face 110 of the stack inorder to partly define an exhaust gallery 126 therebetween. The exhaustgallery 126 enables air to flow from the outlet face 108 of the stack104 to any region of the exhaust port 122 over the top end face 110 ofthe stack 104. It will be appreciated that any air that exits theenclosure 102 through a region 122 b, 122 c of the exhaust port that isnot next to the outlet face 108 of the stack 104 will have passed overthe top end face 110 of the stack 104, thereby further cooling the stack104. This air flow can be seen from the arrows in FIG. 1 b.

The exhaust gallery 126 is defined by the outlet face 108 of the fuelcell stack 104, the top end face 110 of the fuel cell stack 106, abottom surface of the baffle 118, one or more internal side surfaces ofthe enclosure 102, and first and second separation walls 132, 134 thatare discussed in more detail below. The exhaust gallery 126 extendsbetween the outlet face 108 of the stack 104 and the exhaust port 122and is bound, at least in part, by the top end face 110 of the stack104.

The inlet port 120 is provided by the remainder of the opening aroundthe baffle 118; that is, the regions of the opening that are not anexhaust port 122.

A fan 124 is located within the enclosure 102 and sucks air into theenclosure 102 through the inlet port 120. This builds up the airpressure in the enclosure 102 such that air passes into the inlet face106 of the stack, out of the outlet face 108 of the stack 104, and thenout of the exhaust port 122. The combination of the low pressure drop ofthe settling volume in the delivery gallery 128 and the relatively highrestriction offered by the inlet face 106 can promote a uniformlongitudinal (relative to the fuel cell stack 104) air delivery.Although a fan 124 is described for this embodiment, it will beappreciated that any other generator of air flow could be used.

The fan 124 is located in the same plane as the layers of the stack 104.The axis of the fan 124, that is the direction of air flow through thefan, is perpendicular or transverse to the plane of the layers in thestack 104. The axis of the fan 124 is also perpendicular or transverseto the direction of air flow through the stack 104. Aligning the fan 124and stack 104 in this way can provide a compact fuel cell assembly.

The fan 124 sucks air from outside the enclosure 102 into a deliverygallery 128, which may also be referred to as an inlet plenum. In thisexample, fuel cell control system components 130 are located in thedelivery gallery 128. Being able to mount the components 130 in thedelivery gallery 128 can make efficient use of space and thereforeprovide an advantageously small assembly. This can also avoid the needfor a separate inlet plenum chamber (as would usually be employed)allowing for a more compact assembly. In addition, passing the air overthe components 130 can provide for improved cooling of the components130 and potentially pre-heating of the oxidant air, which can improvethe performance of the fuel cell stack 104.

The delivery gallery 128 is defined by the inlet face 106 of the fuelcell stack 104, the bottom end face 112 of the fuel cell stack 106, anumber of internal surfaces of the enclosure 102 and first and secondseparation walls 132, 134 that are discussed in more detail below.

The delivery gallery 128 extends between the inlet port 120 and theinlet face 106 of the stack 104 and is bound, at least in part, by thebottom end face 112 of the stack 104.

The delivery gallery 128 is separated from the exhaust gallery 126 byone or more of the following:

-   -   1. the fuel cell stack 104;    -   2. a first separation wall 132 that extends between the fuel        cell stack 104 and the baffle 118; and    -   3. a second separation wall 134 that extends between the fuel        cell stack 104 and the enclosure 102.

Part of the first separation wall 132 is visible in FIG. 1c and preventsair from passing directly to the exhaust gallery 126 over the top of thestack without passing through cathode flow channels in the stack 104. Inthis example, the first separation wall 132 is generally vertical andextends across the entire width of the stack 104 (orthogonal to theplane of the drawing of FIG. 1c ). On the side of the stack 104 thatincludes the outlet face 108, the left-hand side of the stack 104 shownin FIG. 1b , the first separation 132 wall extends down the side of thestack 104 until it meets the second separation wall 134. This extensionof the first separation wall 132 is not shown in the drawings.

The first separation wall 132 also serves to separate the inlet port 120from the exhaust port 122 around the outside of the baffle 118.

The second separation wall 134 is visible in FIG. 1b and prevents airfrom passing from the delivery gallery 128 to the exhaust gallery 126 upthe side of the stack without passing through cathode flow channels inthe stack 104. In this example, the second separation wall 134 isgenerally horizontal and extends across the entire length of the stack104 (orthogonal to the plane of the drawing of FIG. 1b ). The secondseparation wall abuts the first separation wall 132 at one end and theenclosure 102 at the other end.

The second separation wall 134 is this example has an angled uppersurface 136 such that the region of the exhaust gallery that is adjacentto the outlet face 108 of the stack 104 is a tapering volume. This canguide air flow and/or permit more uniform air flow into the stack 104;the pressure drop across the inlet port 120 to the delivery gallery 128can equalise the air distribution along the stack 104 whilst thepressure drop across each cell of the stack 104 and the asymmetric(tapering) region of the exhaust gallery 126 next to the outlet face 108of the stack, can be used to regulate the flow between cells. This canremove the need for an inlet plenum chamber (as would usually beemployed) allowing for a more compact assembly.

It will be appreciated that the angled upper surface 136 of the secondseparation wall may be curved, straight, a combination of curved andstraight, or any other profile that defines the region of the exhaustgallery that is adjacent to the outlet face 108 of the stack 104 as atapering volume or provides optimal air flow guiding.

Similarly, a portion 138 of the internal surface of the enclosure 102that is next to the inlet face 106 of the stack 104 may be angled suchthat the region of the delivery gallery 128 that is adjacent to theinlet face is a tapering volume. In a similar way to that discussedabove, the asymmetric (tapering) region of the delivery gallery 128 nextto the inlet face 106 of the stack 104 can equalise the compressed airdistribution along the stack 104.

The fuel cell assembly 100 of FIGS. 1a to 1c will now be described witha focus on the air flow through the delivery gallery 128, in particularfirst and second regions 128 a, 128 b of the delivery gallery 128. Itwill be appreciated that one or more of the features of the fuel cellassembly 100 that are described above may be considered as optional whena fuel cell assembly with first and second regions 128 a, 128 b of thedelivery gallery 128, with the associated functionality, is provided.Likewise, the first and second regions 128 a, 128 b of the deliverygallery 128, and the associated functionality, may be considered asoptional for fuel cell assemblies that have one or more of the featuresdescribed above.

The delivery gallery 128 can be considered as having at least tworegions: a first region 128 a and a second region 128 b. An aperture 140is located between the first region 128 a and second region 128 b. Thisaperture 140 may be referred to as a choke aperture. An inlet port 120opens into the first region 128 a in order to provide the air to thedelivery gallery. The second region 128 b is defined, at least in part,by the inlet face 106 of the fuel cell stack.

The delivery gallery 128 and/or aperture 140 are configured such that,in use, air within the first region 128 a of the delivery gallery 128 isturbulent, and air within the second region 128 b of the deliverygallery 128 has a generally uniform pressure. In this way, the randomdistribution of the turbulent air flow in the first region 128 a can beused to cool the fuel cell control system components 130 (or any otherelectronic components) in the first region. Also, the generally uniformair pressure in the second region is applied to the layers in the fuelcell stack in order to provide efficient and effective operation of thefuel cell stack 104.

The aperture 140 may provide a restriction to air flow between the first128 a and second regions 128 b of the delivery gallery 128. The aperture128 may represent a reduction in cross-sectional area in the flow pathof the air from the first region 128 a to the second region 128 b of thedelivery gallery 128. In this way, the air experiences a pressure changeas it flows through the aperture 140 such that a generally uniformpressure is achieved along the length of the fuel cell stack.

In this example, the aperture is partly defined by a side surface of thebottom end face 112 of the fuel cell stack and a protrusion 142 from theinside of a side wall of the enclosure 102. The protrusion 142 extendstowards the bottom end face 112 of the fuel cell stack 104. It will beappreciated that the protrusion 142 need not necessarily be provided aspart of the enclosure 102; it can be formed by an extension of thebottom end face 112 of the stack 104 or any component or member thatprovides the necessary restriction for ensuring that the air within thesecond region 128 b has generally uniform pressure, in use. In someexamples, a protrusion may not be required at all.

It can be advantageous to provide the aperture 140 near the bottom endface 112 of the stack 104. This is because the volume of the firstregion 128 a with turbulent flow is maximised for cooling the components130, whilst only air with a generally uniform pressure is provided tothe inlet face 106 of the stack 104.

Instead of having the protrusion 142 in the vicinity of the bottom endface 112 of the stack 104, a protrusion 144 may be provided in thevicinity of the top end face 110 of the stack 104. This may beparticularly advantageous if the direction of air flow through the stack104 is reversed, for example by reversing the direction of the fan 124,as an aperture defined by the protrusion 144 can provide a regiondownstream of the aperture that has a generally uniform pressure. Inthis example, the aperture is partly defined by a side surface of thetop end face 110 of the fuel cell stack and the protrusion 144 from theinside of a side wall of the enclosure 102. The protrusion 144 extendstowards the top end face 110 of the fuel cell stack 104. This protrusion144 and corresponding aperture may have features and functionality thatcorrespond to the protrusion 142 and corresponding aperture in thevicinity of the bottom end plate 112 that are discussed above.

It will be appreciated that when the direction of flow through the stackis reversed, the face of the stack that is labelled with reference 108will be the inlet face and the ports that are labelled with reference122 will be inlet openings into the enclosure. Therefore, the plenumextending between the components labelled with references 108 and 122can be considered as a delivery gallery having a first region upstreamof the protrusion 144 and a second region downstream of the protrusion144.

One or more of the fuel cell control system components 130, such as aprinted circuit board (PCB), may be considered as a diffuser inasmuch asthey diffuse air that is provided into the first region 128 a of thedelivery gallery in order to impart turbulence on air flow in the firstregion 128 a. The fuel cell control system components 130 can beconsidered as providing for good turbulent flow due to their irregularshape

It will appreciated that the fuel cell control system components 130 canbe considered as fixed with respect to the enclosure 102, that is, theyare not free to move in normal use of the fuel cell assembly 100.Therefore, using the components 130 as a diffuser can provide aconvenient means of imparting turbulence that does not require anymoving parts or active components, which may be more susceptible todamage and may consume power. Furthermore, no additional components arerequired to achieve the desired turbulence. Embodiments disclosed hereincan avoid a need for moving baffles or any additional means forrecirculating the air.

In this example, the axis of the fan 124 is directed towards at least aregion of the components 130. The axis of the fan 124 is not in thedirection of the aperture 140 to the second region 128 b. This candiscourage laminar flow of air from the fan 124 to the second region 128b as the air will be deflected by the components 130 before it reachesthe aperture 140. Therefore, aligning the fan in a specific way canencourage turbulent flow in the first region 128 a. Examples of suchspecific fan alignments include: not pointing towards the aperture 140;transverse to the plane of the layers in the stack 104; perpendicular ortransverse to the direction of air flow through the stack 104;perpendicular or transverse to the principal air flow direction throughthe first region 128 a; and toward one or more components located in thefirst region 128 a of the delivery gallery.

Although the described embodiments show the fan 124 positioned in theinlet flow path providing a somewhat positive air pressure in thedelivery gallery 128, it will be understood that the fan or other airflow generator could be disposed in the exhaust gallery to generate asomewhat negative air pressure therein.

In one or more of the embodiments disclosed herein, at least part of thefirst separation wall 132 may be movable so as to selectively provide anopening between the delivery gallery 128 and the exhaust gallery 126.For example, at least a portion of the first separation wall 132 may befixed to the baffle 118 and may be releasable from the top end face 110of the stack, or at least a portion of the first separation wall 132 maybe fixed to the top end face 110 of the stack and may be releasable fromthe baffle 118. Providing such an opening can enable warm air to berecirculated from the exhaust gallery 126 to the delivery gallery 128.This can provide operational advantages as the air flow through thestack 104 is pre-heated.

At least a portion of the first separation wall 132 may be provided by abimetallic strip such that once the temperature of the air in theexhaust gallery 126 or delivery gallery 128 is above or below athreshold value the metallic strip deforms in order to allow or preventrecirculation. In alternative embodiments, the first separation wall 132may be electrically controlled in accordance with one or more measuredoperating parameters such as air temperature. The first separation wall132 may be made from nitinol.

As will be appreciated from the description of FIGS. 1a to 1c , theaperture 140 in this example extends in a longitudinal direction intothe page of FIG. 1b . In some embodiments, the width of the aperture 140may vary in the longitudinal direction, in order to assist in providinga uniform air pressure in the second region 128 b. The width of theaperture 140 may vary uniformly or non-uniformly in the longitudinaldirection. The aperture 140 may get wider in the longitudinal directionaway from the fan 124. This can further assist in equalising the airpressure in the second region 128 b in spite of the air pressure in thefirst region 128 a on the other side of the aperture 140 being lower atpositions further away from the fan 124.

It will be appreciated that the width of the aperture 140 can be definedby using a protrusion 142 with the requisite size and shape.

It will also be appreciated that the physical properties of any aperturedefined by a protrusion 144 provided in the vicinity of the top end face110 of the stack 104 can have the same characteristics as the aperture140 in the vicinity of the bottom end face 112 of the stack 104.Similarly, the physical properties of a protrusion 144 provided in thevicinity of the top end face 110 of the stack 104 can have the samecharacteristics as the protrusion 142 in the vicinity of the bottom endface 112 of the stack 104.

The dimensions of any aperture or protrusion can be defined so as totune the pressure response of the aperture as air passes from the firstregion 128 a to the second region 128 b.

Throughout the present specification, the descriptors relating torelative orientation and position, such as “top”, “bottom” and “side” aswell as any adjective and adverb derivatives thereof, are used in thesense of the orientation of the fuel cell assembly as presented in thedrawings. However, such descriptors are not intended to be in any waylimiting to an intended use of the described or claimed invention.

The fuel cell assembly disclosed herein may be suitable for a chargerfor portable electronic devices such as mobile telephones, personalcomputing devices and the like.

The invention claimed is:
 1. A fuel cell assembly comprising: anenclosure having a fuel cell stack mounted therein, an inlet openinginto the enclosure, the fuel cell stack having an inlet face forreceiving coolant/oxidant fluid, a delivery gallery extending from theinlet in the enclosure to the inlet face of the fuel cell stack, thedelivery gallery having a first region and a second region separated byan aperture, wherein the delivery gallery and aperture are configuredsuch that, in use, coolant/oxidant fluid within the first region of thedelivery gallery is turbulent, and coolant/oxidant fluid within thesecond region of the delivery gallery has a generally uniform pressure.2. The fuel cell assembly of claim 1 in which the aperture defines arestriction to flow of the coolant/oxidant between the first and secondregions of the delivery gallery.
 3. The fuel cell assembly of claim 1 inwhich the aperture represents a reduction in cross-sectional area in theflow path of the coolant/oxidant flow between the first and secondregions of the delivery gallery.
 4. The fuel cell assembly of claim 1 inwhich the aperture is defined, at least in part, by a bottom end face ofthe fuel cell stack.
 5. The fuel cell assembly of claim 4 in which theaperture is defined, at least in part, by a protrusion extending towardsthe bottom end face of the fuel cell stack.
 6. The fuel cell assembly ofclaim 5 in which the protrusion extends away from an internal wall ofthe enclosure.
 7. The fuel cell assembly of claim 6 in which theprotrusion comprises part of an internal wall of the enclosure.
 8. Thefuel cell assembly of claim 1 in which the aperture extends in alongitudinal direction and the width of the aperture varies in thelongitudinal direction.
 9. The fuel cell assembly of claim 8 in whichthe aperture gets wider in the longitudinal direction away from a fan orair flow generator.
 10. The fuel cell assembly of claim 1 furthercomprising a diffuser within the first region of the delivery gallery,the diffuser configured to impart turbulence on oxidant I coolantreceived from the inlet of the enclosure.
 11. The fuel cell assembly ofclaim 10 in which the diffuser is fixed such that it is not free to movein normal use of the fuel cell assembly.
 12. The fuel cell assembly ofclaim 10 in which the diffuser comprises one or more fuel cell controlsystem components.
 13. The fuel cell assembly of claim 1, furthercomprising a fan located within the enclosure configured to cause thecoolant/oxidant to be transferred from the inlet in the enclosure to theinlet face of the fuel cell stack.
 14. The fuel cell assembly of claim13 in which the axis of the fan is directed away from the aperture. 15.The fuel cell assembly of claim 13 in which the axis of the fan isdirected towards at least a region of fuel cell control system.
 16. Thefuel cell assembly of claim 13 in which the axis of the fan istransverse to the plane of the layers in the stack.
 17. The fuel cellassembly of claim 13 in which the axis of the fan is transverse to thedirection of coolant/oxidant flow through the stack.
 18. The fuel cellassembly of claim 13 in which the axis of the fan is transverse to theprincipal air flow direction through the first region.
 19. The fuel cellassembly of claim 1, further comprising a separation wall configured toseparate the delivery gallery from an exhaust gallery, wherein at leastpart of the separation wall is movable so as to selectively provide anopening between the delivery gallery and the exhaust gallery.
 20. Thefuel cell assembly of claim 19, wherein the at least part of theseparation wall is moveable in accordance with the temperature of thecoolant/oxidant in the exhaust gallery and/or delivery gallery.